This invention relates to beacon based collision avoidance systems (BCAS) for aircraft and more particularly to such systems which require a minimum of ground sites and whereby data which can be used to calculate collision threat is obtained.
The problem of preventing mid-air collisions of aircraft has long confronted the aircraft industry generally. This problem has recently become more acute with the introduction of relatively large and expensive aircraft each of which is capable of carrying great numbers of passengers. The public has come to expect that the aviation industry provide comprehensive flight services with a high degree of safety and the industry has striven to provide it. It is, however, now recognized that the conventional air traffic control (ATC) system suffers from rather severe limitations with respect to mid-air collision prevention because of the constantly increasing volume of air traffic. Under conventional ATC standards each airborne aircraft under control is assigned an exclusive volume of air space about the aircraft. As the density of traffic increases and air speeds rise, the volume of space that must be assigned to each controlled aircraft must also be increased to provide an adequate margin or periphery of safety about each aircraft, and all aircraft need to be placed under positive control.
There is now considerable interest in techniques for providing aircraft with auxiliary information which will support a back-up to the ATC system so that appropriate collision avoidance maneuvers can be made in the event of ATC system error or malfunction or pilot error and/or to bring aircraft not under positive control into the avoidance system. Various back-up collision avoidance systems have been proposed, one of which, the beacon collision avoidance system (BCAS) is of particular interest at the present time since it affords immediate protection of the BCAS equipped aircraft from all ATCRBS transponder equipped aircraft. The present invention comprises an improvement over other forms of BCAS systems. BCAS is characterized in that each protected aircraft has on-board equipment which considers the responses of intruder aircraft within its field of interest to interrogations from a standard ground air traffic control beacon system interrogator (ATCBI). Where there are two spaced apart ground ATCBI stations interrogating the particulaar field of interest, it has been claimed that the protected aircraft can determine with a relatively high degree of accuracy the position of intruder aircraft with respect to the protected aircraft and thus provide itself with collision avoidance information.
The same basic technique may also be used on the ground to provide passive (non-interrogating) surveillance using the reply signals generated to nearby active interrogators. In this application the amount of interference generated at the beacon frequencies (1030 and 1090 MHz) is held constant permitting an increase in the number of control facilities without increasing interference.